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Start here
- [eGFR calculator](/egfr-calculator) estimates kidney function from creatinine, age and sex using the race-free CKD-EPI 2021 equation.
- [GFR levels and CKD stages](/gfr-levels) explains what each eGFR band means, the KDIGO heat map that combines eGFR with urine albumin, and how eGFR normally changes with age.
- [High creatinine](/high-creatinine) walks through what a raised creatinine means, how to tell acute from chronic changes using the KDIGO AKI criteria, and common non-kidney causes such as muscle mass and supplements.
- [BUN/creatinine ratio](/bun-creatinine-ratio-calculator) helps separate dehydration and other "pre-renal" causes from problems within the kidney.
Which kidney tool do you need?
Kidney function is usually assessed with a blood creatinine test, an estimated glomerular filtration rate (eGFR) and a urine albumin test. The tools in this section cover each step:
- [eGFR calculator](/egfr-calculator) – the CKD-EPI 2021 equation, used to diagnose and stage chronic kidney disease (CKD).
- [Creatinine clearance calculator](/creatinine-clearance-calculator) – the Cockcroft-Gault equation, still used for many drug-dosing decisions.
- [Creatinine converter](/creatinine-mg-dl-to-umol-l) – mg/dL ↔ µmol/L (factor 88.4).
- [BUN to urea converter](/bun-to-urea-converter) – US BUN in mg/dL ↔ urea in mmol/L.
- [BUN/creatinine ratio calculator](/bun-creatinine-ratio-calculator) – a clue to dehydration and other causes of raised urea.
- [Urine albumin-to-creatinine ratio converter](/urine-albumin-creatinine-ratio-mg-g-to-mg-mmol) – mg/g ↔ mg/mmol, with albuminuria categories.
- [Uric acid converter](/uric-acid-mg-dl-to-umol-l) – mg/dL ↔ µmol/L, relevant to gout and kidney stones.
CKD staging at a glance
| GFR category | eGFR (mL/min/1.73 m²) | Description |
|---|---|---|
| G1 | 90 or more | Normal or high |
| G2 | 60–89 | Mildly decreased |
| G3a | 45–59 | Mildly to moderately decreased |
| G3b | 30–44 | Moderately to severely decreased |
| G4 | 15–29 | Severely decreased |
| G5 | below 15 | Kidney failure |
| Albuminuria category | UACR (mg/g) | UACR (mg/mmol) |
|---|---|---|
| A1 | below 30 | below 3 |
| A2 | 30–300 | 3–30 |
| A3 | above 300 | above 30 |
CKD is diagnosed when eGFR is below 60, or when there are markers of kidney damage such as albuminuria, for more than three months. KDIGO stages CKD by both the GFR and albuminuria categories, because together they predict the risk of kidney failure and cardiovascular disease much better than either alone.
eGFR or creatinine clearance?
eGFR is normalised to a standard body surface area and is used for diagnosis and staging. Creatinine clearance from Cockcroft-Gault uses body weight and is not normalised; many drug labels specify it for dose adjustment. In older, smaller people the two can differ substantially – an 85-year-old woman weighing 50 kg with a creatinine of 1.0 mg/dL has an eGFR of about 55 but a creatinine clearance of about 33 mL/min.
What affects creatinine
Creatinine comes from muscle, so muscle mass, diet (especially cooked meat and creatine supplements), some medicines (such as trimethoprim) and hydration all influence it. When creatinine-based eGFR may be misleading, KDIGO recommends measuring cystatin C and using a combined equation.
Protecting kidney function
Key measures include controlling blood pressure and blood sugar, using ACE inhibitors or ARBs when albuminuria is present, SGLT2 inhibitors for most people with CKD, avoiding regular use of non-steroidal anti-inflammatory drugs, staying active and not smoking. People with diabetes should have kidney tests at least yearly; our A1C calculator helps track glucose control.
When to seek medical advice
See a clinician if your eGFR is below 60, if it has fallen noticeably since your last test, or if your urine shows albumin. Seek prompt care for markedly reduced urine output, swelling, breathlessness, persistent nausea or confusion.
Frequently asked questions
Is an eGFR of 60–89 kidney disease?
Not on its own. It is common with ageing and counts as CKD only if there are other signs of kidney damage, such as albuminuria.
Why do I need a urine test if my eGFR is normal?
Albumin in the urine can be the earliest sign of kidney damage, especially in diabetes and high blood pressure.
Can kidney function improve?
Results can improve when dehydration, illness or medicine effects resolve. In established CKD, treatment aims to slow decline.
Sources
- Inker LA, et al. New Creatinine- and Cystatin C-Based Equations to Estimate GFR without Race. N Engl J Med 2021
- KDIGO 2024 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease
- Cockcroft DW, Gault MH. Prediction of creatinine clearance from serum creatinine. Nephron 1976